The games that are most likely to come to Linux first are Left 4 Dead 2 and Team Fortress 2. Porting other Source-engine based games that already run on Mac shouldn't be too big of a problem - I personally expect CS:GO and Dota2 to follow after L4D2 and TF2.I don't know of any official statements talking about games though.

I hope Valve will offer a native port of CS:GO for GNU/Linux as fast as possible.It would be nice to see CS1.6 ported to GNU/Linux, just for the history books. Benefit: Quake1/2 runs since many years under Linux, uses OpenGL since the first day and doesn't need much graphic power (good for open-source drivers. especially older Intel).

I think the plan is to test the system before opening up each and every game. Each game requires slightly different tweaking to get running. Steam Linux might not launch with your favorite games but +1 for first steps.

I hope Valve will offer a native port of CS:GO for GNU/Linux as fast as possible.It would be nice to see CS1.6 ported to GNU/Linux, just for the history books. Benefit: Quake1/2 runs since many years under Linux, uses OpenGL since the first day and doesn't need much graphic power (good for open-source drivers. especially older Intel).